New York-based medical appointment business ZocDoc has raised a huge amount of cash and has good traction in its space. But the company has now revealed that it has drawn $2 million of a new $55 million convertible debt note.

So why is it looking for the capital now?

“We’ve always said it’s best to raise money when we don’t need it,” CEO and founder Cyrus Massoumi told me today. “It’s just about bolstering up the balance sheet.”

I pressed Massoumi a bit further on the question of why, but he insisted that there was “no strategic reason” for the move.

“People are beating at the door to work here or give us money,” Massoumi said.

But, of course, the company will continue fighting for growth and to fend off competitors. The cash will be helpful for that.

As we’ve written before, ZocDoc now has more than 400 employees. Its New York office has recently expanded to include another floor and its relatively new Pheonix office now has more than 15 employees. ZocDoc expects that the Phoenix office will grow quickly and accommodate “more than 600 area residents” in the next fives years.

It’s also had nice growth in the past year. Medical appointment bookings are up 200 percent year over year and medical bookings made on mobile devices are up 500 percent year over year. In January, ZocDoc was seeing 2.5 million unique visitors per month on the web and mobile. The company said it isn’t quite at 3 million uniques per month yet.

As for its reach, ZocDoc is live in more than 35 major metropolitan areas and covers 1800 towns total. Medical professionals pay $300 a month to use the service and patients don’t pay a thing to book appointments. ZocDoc recently surpassed 1,000 different types of procedures in its bookings. And medical professionals from 42 different types of specialties are represented on the service.

“We’re only serving 40 percent of the U.S.,” Massoumi said. “We have 60 percent to go.”

ZocDoc only serves doctors and patients in the U.S., so international expansion could easily be on the company’s road map and the convertible note would help with that. I asked Massoumi directly if he has plans to take ZocDoc international in the next year, but he deflected.

“We’re only focused on growing domestically right now,” Massoumi said.

ZocDoc was founded in 2007 and has $95 million in funding to date. Investors include Goldman Sachs, Khosla Ventures, DST Global, Marc Benioff, and Jeff Bezos.